Axially extending electric machine electronics cooling tower

ABSTRACT

An electronic package adapted for connection to a rear frame member of an electric machine. The electronic package includes a cooling tower having first and second axial ends. The cooling tower includes a metallic wall defining radially inner and outer wall surfaces and extending about the package central axis. The radially inner wall surface defines an axially extending air passage through the cooling tower with an inlet proximate the first axial end. Spaced metallic ribs are in conductive thermal communication with the radially inner wall surface traverse and the air passage. Power electronics devices are attached in conductive thermal communication to the radially outer wall surface. The cooling tower provides a heat sink for the power electronics devices with a primary cooling path for each of the power electronics device extending radially inwardly to the cooling tower. An electric machine including such an electronic package is also disclosed.

PRIORITY CLAIM AND CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/061,379 entitled AXIALLY EXTENDING ELECTRIC MACHINEELECTRONICS COOLING TOWER, filed Oct. 8, 2014; and is related to U.S.patent application Ser. No. ______ entitled DUAL AIR AND LIQUID COOLINGMEDIA COMPATIBLE ELECTRIC MACHINE ELECTRONICS, filed ______ , 2015(Attorney Docket No. 22888-0237); U.S. patent application Ser. No.______ entitled BI-DIRECTIONAL MOSFET COOLING FOR AN ELECTRIC MACHINE,filed ______ , 2015 (Attorney Docket No. 22888-0241); U.S. patentapplication Ser. No. ______ entitled CIRCUIT LAYOUT FOR ELECTRIC MACHINECONTROL ELECTRONICS, filed ______ , 2015 (Attorney Docket No.22888-0243); U.S. patent application Ser. No. ______ entitled CENTRALLYLOCATED CONTROL ELECTRONICS FOR ELECTRIC MACHINE, filed ______ , 2015(Attorney Docket No. 22888-0245); U.S. patent application Ser. No.______ entitled PEDESTAL SURFACE FOR MOSFET MODULE, filed ______ , 2015(Attorney Docket No. 22888-0247); and U.S. patent application Ser. No.______ entitled RADIALLY ADAPTABLE PHASE LEAD CONNECTION, filed ______ ,2015 (Attorney Docket No. 22888-0249), the entire disclosures of whichare incorporated herein by reference.

BACKGROUND

Vehicles, such as those employing an internal combustion engine and/orhaving a hybrid drive train that includes an electric machine, oftenemploy what are commonly referred to as alternators.

Vehicle alternators are electric machines that selectively function as agenerator or an electric motor. In conventional internal combustionengine drive vehicles, alternators are employed as an electric motor toprovide torque to the engine when starting the engine. After the enginehas been started, the alternator can function as a generator to generatecurrent to recharge the vehicle battery. In hybrid vehicles, thealternator may be used as an electric motor to additionally providetorque for driving the vehicle.

The electrical circuitry employed with alternators can generatesignificant heat that must be dissipated. As modern vehicles placegreater demands on alternators, the demands on the alternator circuitryalso increases. Improvements which address the increased demands onelectric machines such as those which are used as vehicle alternatorsare desirable.

SUMMARY

The present invention provides an electronic package for an electricmachine wherein the electronic packages has a cooling tower structurethat enhances the functionality of the electric machine.

The invention comprises, in one form thereof, an electronic packageadapted for connection to a rear frame member of an electric machine.The electronic package includes a cooling tower having opposite firstand second axial ends spaced along a package central axis. The coolingtower includes a metallic wall extending about the package central axisto define a radially inner wall surface and a radially outer wallsurface. The radially inner wall surface defines an axially extendingair passage through the cooling tower wherein the air passage has aninlet proximate the first axial end. The cooling tower also includes aplurality of spaced metallic ribs in conductive thermal communicationwith the radially inner wall surface wherein the ribs traverse the airpassage. A plurality of power electronics devices are attached inconductive thermal communication to the cooling tower atcircumferentially distributed positions on the radially outer wallsurface. The cooling tower provides a heat sink for heat loss from thepower electronics devices with a primary cooling path for each of thepower electronics device extending radially inwardly to the coolingtower.

In some embodiments of the electronic package, the electronic packagefurther includes a plurality of power modules wherein each power moduleincludes at least one power electronics device, a base in conductivethermal communication with the radially outer wall surface and ametallic cover plate. The cover plate has an interior surfacesuperposing the base and an exterior surface oriented radially outwardand unobstructedly exposed to ambient air surrounding the electronicpackage wherein heat loss from each power module is transferred alongthe first cooling path and along a secondary cooling path extendingradially outwardly through the cover plate and to ambient air. Forexample, the module cover plates may be configured with fins wherebyconvective heat transfer therefrom is enhanced.

In some embodiments of the electronic package, the electronic packagefurther includes a plurality of power modules including the plurality ofpower electronics devices wherein each power module includes a basedefining a surface that abuttingly engages the radially outer wallsurface whereby the base and the cooling tower wall are in conductivethermal communication with the engaging surfaces extending substantiallyparallel with the package central axis. In such an embodiment, theplurality of metallic ribs may extend directly from circumferentiallocations on the radially inner wall surface that are directly radiallyinward of the power modules. In yet another variant of such anembodiment, the radially outer wall surface may define a plurality ofplanar mounting surfaces, each planar mounting surface engaging the basesurface of a respective power module, each planar mounting surfaceparallel with the package central axis. In such a variant, each planarmounting surface may be oriented tangentially relative to an imaginarycircle concentric with and oriented perpendicularly relative to thepackage central axis.

In some embodiments of the electronic package, the wall and the ribs areintegrally formed portions of the cooling tower.

In some embodiments of the electronic package, the electronic packagefurther includes electronic control circuitry operatively connected tothe power electronics devices wherein the electronic control circuitryis substantially surrounded by the plurality of power electronicsdevices. In such an embodiment, the control circuitry may besubstantially thermally isolated from the heat loss from the powerelectronics devices.

In some embodiments of the electronic package, the power electronicsdevices are substantially evenly distributed about the radially outerwall surface.

In some embodiments of the electronic package, the power electronicsdevices are equidistance along the package central axis from animaginary plane perpendicular to the package central axis.

Another embodiment takes the form of an electric machine that includes astator defining a machine central axis, a rotor surrounded by androtatable relative to the stator about the machine central axis, a rearframe member rotatably fixed relative to the stator and through whichthe machine central axis extends and an electronic package as describedherein wherein the machine central axis extends through the electronicpackage and the cooling tower is connected to the rear frame member.

In some embodiments of the electric machine, the machine central axisand the package central axis coincide.

In some embodiments of the electric machine, the electric machine isair-cooled and the rear frame member has an aperture through whichcooling air flow is drawn generally axially, in the direction of therotor relative to the electronic package, for cooling the electricmachine at locations downstream of the aperture. The air passage has anoutlet proximate the second axial end and the air passage outlet is influid communication with the rear frame member aperture. Cooling airflow is drawn into the air passage inlet and through the air passagewhereby convective heat transfer along the primary cooling path occursbetween the cooling tower wall and ribs and the cooling air flow alongthe air passage. The cooling air flow also proceeds through the airpassage outlet and the rear frame member aperture for cooling theelectric machine at locations downstream of the aperture. In such anembodiment, the electric machine may further include a fan rotatablewith the rotor about the central axis, wherein the air flow through theaperture is induced by fan rotation.

In some embodiments of the electric machine wherein the electric machineis liquid-cooled and the rear frame member defines a metallic wallextending substantially perpendicularly relative to the machine centralaxis, the rear frame member wall has an inner axial side in contact withliquid coolant and an opposite outer axial side in conductive thermalcommunication with the cooling tower wherein conductive heat transferoccurs between the cooling tower and the rear frame member wall andconvective heat transfer occurs between the rear frame member wall andthe liquid coolant.

In some embodiments of the electric machine, the electric machinefurther includes a plurality of power modules including the plurality ofpower electronics devices wherein each power module includes a base inconductive thermal communication with the radially outer wall surface,and a metallic cover plate, the cover plate having an interior surfacesuperposing the base and an exterior surface oriented radially outwardand unobstructedly exposed to ambient air surrounding the electronicpackage wherein heat loss from each power module is transferred alongthe first cooling path and along a secondary cooling path extendingradially outwardly through the cover plate and to ambient air. In suchan embodiment, the module cover plates may be configured with finswhereby convective heat transfer therefrom is enhanced.

In some embodiments of the electric machine, the electric machinefurther includes a plurality of power modules including the plurality ofpower electronics devices wherein each power module comprises a basedefining a surface that abuttingly engages the radially outer wallsurface whereby the base and the cooling tower wall are in conductivethermal communication with the engaging surfaces extending substantiallyparallel with the machine central axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects, features and attendant advantages of the presentinvention will become fully appreciated as the same becomes betterunderstood when considered in conjunction with the accompanyingdrawings. Although the drawings represent embodiments of the disclosedapparatus, the drawings are not necessarily to scale or to the samescale and certain features may be exaggerated or omitted in order tobetter illustrate and explain the present disclosure. Moreover, inaccompanying drawings that show sectional views, cross-hatching ofvarious sectional elements may have been omitted for clarity. It is tobe understood that this omission of cross-hatching is for the purpose ofclarity in illustration only.

FIG. 1 is a side view of an alternator embodiment according to the priorart;

FIG. 2 shows a typical layout of a prior alternator's power and controlelectronics, disposed on the back face of the alternator's rear framemember;

FIG. 3 is an electrical schematic of a typical alternator's powerelectronics;

FIG. 4 is a side view of an alternator including an embodiment of anintegrated electronics assembly or “electronic package” according to thepresent disclosure mounted on the back face of the alternator's rearframe member;

FIG. 5 is a rear perspective view of an electronic package according tothe present disclosure showing paths of air flow and forced convectionareas, and areas of natural convection;

FIG. 6 is another rear perspective view of the electronic package ofFIG. 5;

FIG. 7 is another rear perspective view of the electronic package ofFIG. 5;

FIG. 8 shows air-cooling of the integrated electronics utilizing therearmost of dual internal fans in an electric machine embodimentaccording to the present disclosure;

FIG. 9 shows air-cooling of the integrated electronics utilizing anexternal front fan and/or peripheral airflow in an electric machineembodiment according to the present disclosure;

FIG. 10 shows liquid-cooling and air-cooling of the integratedelectronics in an electric machine embodiment according to the presentdisclosure;

FIG. 11 is an axial rear view of the electronic package of FIG. 5 withits cover removed;

FIG. 12 is a rear perspective view of the electronic package as shown inFIG. 11;

FIG. 13 is another rear perspective view of the electronic package asshown in FIG. 11, showing the ingress of cooling air;

FIG. 14 is another rear perspective view of the electronic package asshown in FIG. 11, shown oriented as mounted to the rear frame member ofan electric machine (not shown) in a normal installed position, showingsplash drainage paths;

FIG. 15 is a front perspective view of the electronic package of FIG.14, showing the axial end of the electronic package that interfaces withthe rear frame member of the electric machine (not shown), showingsplash drainage paths;

FIG. 16 is an axial rear view of the electronic package, similar to thatof FIG. 11, showing radially inward conductive heat flow from the itspower electronics modules to its main, cooling tower heat sink along aprimary cooling path;

FIG. 17 is a rear perspective view of the electronic package, similar tothat of FIG. 13, but with the control electronics assembly and B+terminal omitted;

FIG. 18 is a rear perspective view of the cooling tower of theelectronic package of FIG. 5;

FIG. 19 is a rear perspective view of the interconnected MOSFET modulesof the electronic package of FIG. 5, arranged relative to each other intheir installed positions;

FIG. 20 is an axial rear view of the cooling tower of FIG. 18;

FIG. 21 is another rear perspective view of the cooling tower of FIG.18;

FIG. 22 is a side view of the cooling tower of FIG. 18;

FIG. 23 is a partial and partly sectioned view of a liquid-cooledembodiment of an electric machine according to the present disclosure,showing heat flow through the cooling tower towards the machine's rearframe member;

FIG. 24 is an axial rear view of the electronic package as shown in FIG.17, showing bi-directional heat flow from the MOSFET modules, andindicating the positions of some power electronics devices within themodules;

FIG. 25 is a rear perspective view of the cooling tower of FIG. 18;

FIG. 26 is a rear perspective view of electronic package of FIG. 13,with the covers of the power electronics module housings removed;

FIG. 27 is a rear perspective view of the interconnected MOSFET modulesof FIG. 19 without their covers;

FIG. 28 is a fragmented, partial rear perspective view of theinterconnected MOSFET modules of FIG. 27, showing their powerelectronics devices and electrically insulative (T-Clad) base layers;

FIG. 29 is a cross-sectional view of a MOSFET module along line 29-29 ofFIG. 28;

FIG. 30 is a fragmented, rear perspective view showing an electricmachine according to the present disclosure having an electronic packageand a rear frame member of large diameter, with a phase lead wireexiting the frame member at a location radially outward of itsconnection point to its respective MOSFET module phase terminal;

FIG. 31 is a fragmented, rear perspective view showing an electricmachine according to the present disclosure having, relative to theelectric machine of FIG. 30, an identical electronic package and a rearframe member of relatively small diameter, with a phase lead wireexiting the frame member at a location radially inward of its connectionpoint to its respective MOSFET module phase terminal;

FIG. 32 is a fragmented front perspective view of a portion of anelectronic package embodiment according to the present disclosure,showing a recess or slot in the cooling tower between acircumferentially adjacent pair of MOSFET modules, through which a phaselead wire exiting a hole in a small diameter rear frame member (notshown) may be routed to its respective MOSFET module phase terminal;

FIG. 33 is a fragmented, rear perspective view showing an electricmachine according to the present disclosure having an electronic packageand a rear frame member whose back face is provided with a void by whichthe radial position at which the phase lead wire exits the frame membermay be adapted to that of the MOSFET module phase terminal;

FIG. 34 is a view of the MOSFET module housing covers omitted from FIG.27, arranged in their installed positions, showing the respective,integral bosses extending radially inward from the interior surfaces ofthe cover;

FIG. 35 is an axial view of a MOSFET module showing its respective powerelectronics devices, module housing cover, and the cover's integralbosses extending radially inward from the interior surface of the cover,with the module housing sidewalls omitted for clarity;

FIG. 36 is a rear perspective view of the electronic package as shown inFIG. 17, with portions of the MOSFET modules radially inward of theirhousing covers omitted, showing the bi-directional heat sinks of anelectronic package according to the present disclosure, and paths ofheat transfer from each MOSFET module into the main, cooling tower heatsink by conduction along a primary cooling path, and to ambient air vianatural convection from the module housing covers along a parallel,secondary cooling path;

FIG. 37 is a rear perspective view of the main heat sink of the coolingtower, the control electronics assembly with circuits boards shown butlid or cover plate omitted, and the control electronics signal leads, ofan electronic package embodiment according to the present disclosure;

FIG. 38 is a rear perspective view similar to that of FIG. 37, but withthe control electronics assembly removed;

FIG. 39 is a rear perspective view similar to that of FIG. 37, but withthe lid or cover plate of the control electronics assembly, and thecircuit board portion located on the interior face thereof, omitted,showing the interior of the plastic cup or receptacle and controlelectronics circuit board portions mounted therein;

FIG. 40 is a rear perspective view similar to FIG. 18, showing only themain heat sink and the centrally located well thereof in which theplastic cup or receptacle of the control electronics assembly isnormally contained;

FIG. 41 is a rear perspective view of the control electronics assemblyand the signal leads of an electronic package embodiment according tothe present disclosure;

FIG. 42 is a front perspective view of the signal leads and the lid orcover plate and of the control electronics assembly shown in FIG. 41,showing the control electronics circuit board portion disposed on theinterior surface of the lid;

FIG. 43 is a rear perspective view of the control electronics assemblyand signal leads shown in FIG. 41, with the lid or cover plate of theplastic cup removed, showing the circuit board portion normally disposedon the interior surface of the lid;

FIG. 44 is a rear perspective view of the control electronics assemblyand signal leads as shown in FIG. 43, but with the circuit board portionnormally disposed on the interior surface of the lid or cover plateomitted, showing the interior of the plastic cup and control electronicscircuit board portions mounted therein;

FIG. 45 is a rear perspective view of a portion of a control electronicsassembly embodiment as shown in FIG. 39;

FIG. 46 is a side perspective view of the control electronics assemblyportion of FIG. 45, with its circuit board portions omitted, showingonly its plastic cup;

FIG. 47 is a rear perspective view of the plastic cup of FIG. 45,showing the cup interior;

FIG. 48 is another rear perspective view of the plastic cup of FIG. 45,showing the cup interior;

FIG. 49 is a front perspective view of the plastic cup of FIG. 45,showing the recess in which are normally disposed the electric machineshaft end and brush holder;

FIG. 50 is another front perspective view of the plastic cup of FIG. 45;

FIG. 51 is a rear perspective view of the circuit board portions andsignal leads shown in FIG. 44;

FIG. 52 is a rear perspective view of an alternative embodiment of thecircuit board portions and signal leads shown in FIG. 51, wherein thesignal leads and the circuit board material on which control circuitportions are disposed, are integral with each other, and defined by aplastically deformed singular flexible circuit board material piece,also showing optional, additional circuit board portions in dashedlines;

FIG. 53 is a plan view of the singular flexible circuit board materialpiece of FIG. 52 in its undeformed state, also showing the optional,additional circuit board portions in dashed lines;

FIG. 54 is a plan view of a nested plurality of undeformed flexiblecircuit board and signal lead material pieces arranged in a plane forshipping or assembly;

FIG. 55 is rear perspective view of the electronic package embodiment ofFIG. 7 with its cover omitted;

FIG. 56 is a rear perspective view of an alternative cooling towerembodiment provided with radially extending pedestals defining mountingsurfaces for MOSFET modules;

FIG. 57 is a fragmented front perspective view of an electronic packageincluding the cooling tower embodiment of FIG. 56;

FIG. 58 is a sectional view along line 58-58 of FIG. 11, modified toinclude the cooling tower embodiment of FIG. 56, showing locations ofgutters/ledges along cooling tower pedestal edges for splash drainage;

FIG. 59 is an enlarged view of rectangular outlined area 59 of FIG. 58,showing gutters/ledges along cooling tower pedestal edges for splashdrainage;

FIG. 60 is a fragmentary, rear perspective view of a portion of theelectronic package including the cooling tower embodiment of FIG. 56,showing gutters/ledges along cooling tower pedestal edges for splashdrainage;

FIG. 61 is another fragmentary, rear perspective view of a portion ofthe electronic package of FIG. 60, showing gutters/ledges along coolingtower pedestal edges for splash drainage;

FIG. 62 is an enlarged, fragmented sectional view along line 62-62 ofFIG. 11, modified to include the cooling tower embodiment of FIG. 56,showing the gutter/ledge along the rear edge of an example pedestal forsplash drainage; and

FIG. 63 is an enlarged, fragmented front perspective view betweencircumferentially adjacent MOSFET modules of an electronic packageembodiment of the present disclosure including the cooling towerembodiment of FIG. 56, showing gutters/ledges for splash drainage.

Corresponding reference characters indicated corresponding partsthroughout the several views. Although the drawings representembodiments of the disclosed apparatus, the drawings are not necessarilyto scale or to the same scale and certain features may be exaggerated inorder to better illustrate and explain the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

The invention is adaptable to various modifications and alternativeforms, and the specific embodiments thereof shown by way of example inthe drawings is herein described in detail. The exemplary embodiments ofthe present disclosure are chosen and described so that others skilledin the art may appreciate and understand the principles and practices ofthe present disclosure. It should be understood, however, that thedrawings and detailed description are not intended to limit theinvention to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

It shall be understood that the terms “radial” and “axial” are generallyused herein to establish positions of individual components relative tothe central axis of an electric machine or electronic package, ratherthan an absolute position in space. Further, regardless of the referenceframe, in this disclosure terms such as “parallel” and “perpendicular”and the like are not used to connote exact mathematical orientations orgeometries, unless explicitly stated, but are instead used as terms ofapproximation. Terms such as “forward,” “rearward,” “front,” and “rear”and the like are used in the context of the central axis extendingbetween opposite front/forward and rear/rearward axial ends. Further, itshould be understood that various structural terms used throughout thisdisclosure and claims should not receive a singular interpretationunless it is made explicit herein.

Although the disclosed embodiment relates to three-phase or six-phase(i.e., dual three-phase) synchronous machine topologies such as clawpole alternators and internal permanent magnet hybrid machines, thepresent disclosure could also be applied to other machine topologiessuch as switched reluctance or induction. Those having ordinary skill inthe art will understand the above-mentioned six-phase (i.e., dualthree-phase) machines are of the type having two, three-phase windingsthat are 30 degrees electrically apart for noise cancellation, as shownin FIG. 3. It is to be understood, however, that all aspects of thedisclosure provided herein also relate and could be applied to puresix-phase machines as well as to five-phase machines or seven-phasemachines, which are electric machine types well-known to those havingordinary skill in the relevant art.

The electric machine embodiments 130 exemplified herein have an intendedpower range of 1.5 to 17 kW, a voltage range of 12-60V, and statoroutside diameters ranging between 120 and 200 mm. Referring to FIG. 4,the exemplary electronic package embodiments 132 disclosed herein areintegrated electronic assemblies packaged as separable electric machinecomponents adapted for being mounted to a rear frame member 134 of anelectric machine 130, at the axially rearmost portion of the machine,relative to the machine's normal orientation as typically installed.Typically, the rear frame of an electric machine radially and axiallysupports the rotor shaft 136 relative to the machine central axis 138through a bearing. The rotor 140 may itself define the machine centralaxis 138, as may the stator 142. Integrated control and powerelectronics for electric machines are commonly located rearward of thestator and rotor, and mounted to the rear frame. A prior electricmachine 100 including its integrated control and power electronicspackage 114 is shown in FIG. 1.

Cooling of the integrated electronics of prior electric machinestypically relies at least in part on the means provided for coolingother components of the machine located internally of the machinehousing, such as the stator windings or the rotor. Certain aspects ofthe invention(s) disclosed herein relate to the electronic package beingmounted at the rear of an electric machine.

The rear frame may include a member 134 defining a generally planar backface 144 that extends perpendicularly relative to the central axis 138.Liquid-cooled electric machines often provide a liquid coolant passageor water jacket portion 146 in the rear frame, located axially insidethe back face 144. Such a machine according to the present disclosure isshown in FIG. 10.

Referring to FIG. 8, the rear frame member 134 may house one of a pairof internal fans 148 rotatable with the rotor 140. The rear fan 148induces air flow in a forward direction from the rear of the machine130, axially inwardly towards the rotor 140, through apertures 150 inthe rear frame member 134. Air drawn axially into the internal rear fan148 is directed radially outwardly, usually past the stator windingswhich are cooled thereby, and expelled radially from the machine 130.

Referring to FIG. 9, some electric machine embodiments 130 utilize anexternal fan (not shown), rotatable with the rotor 140 and locatedaxially forward of the stator 142, to draw air through openings in themachine housing. The external fan induces a forwardly directed air flowthrough apertures 150 in the rear frame member 134 and past the statorand the rotor.

Referring to FIGS. 5 and 6, the spatial arrangement of the components inan electronic package 132 according to the present disclosure maximizesthe use of available package space. The exemplary embodiments providepower electronics devices 154 as power modules 154 or MOSFET modules 154providing two parallel sets 156 a, 156 b of three-phase MOSFETrectifier/inverters 154, as shown in FIG. 3. Prior electric machine 100designs (see, e.g., FIGS. 1 and 2) representative of the current stateof the art physically do not allow paralleling the power electronicdevices. These prior machines utilize three MOSFET modules 116 arrangedalong with the control electronics 118 on the back face 112 of the rearframe 110, generally as shown in FIG. 2. The lack of physical roomavailable at this site precludes packaging paralleled MOSFETrectifiers/inverters there. Contradistinctively, electric machineembodiments 130 according to the present disclosure accommodate thepackaging of six MOSFET modules 154, provided as two parallel-connectedsets 156 a, 156 b of three modules 154 as shown in FIG. 3. Relative tothe power electronics 116 of current state of the art machines 100 ofsimilar capacity, these two sets 156 a, 156 b of power modules 154effectively reduce the current therethrough by approximately half, sincethey are in parallel.

In the example of a three-phase electric machine 130 that operates in agenerating mode to produce 200A of DC output current, a machine 100designed according to the current state of the art would have 200Aflowing through each of its three MOSFET modules 116 for ⅓ of the timeto rectify the stator output, whereas a machine 130 according to anembodiment of the present disclosure each MOSFET module 154 need onlyrectify 200A/2 or 100A. MOSFET loss is an ohmic type loss whereby theheat loss is proportional to current squared. Thus, compared to theprior state of the art electric machine 100, an electric machine 130according to the present disclosure, owing to its paralleled powerelectronics devices 154, effectively cuts the power loss in each powerelectronics device 154 by ¼^(th) (i.e., by ½²) and the overall heat lossin the power electronics in half (i.e., ¼×2=½), a result providingsignificant advantages vis-à-vis comparable prior electric machines 100.

Referring to FIGS. 1 and 2, in a typical prior air-cooled electricmachine 100, the cooling air enters axially into the rear of themachine. However, the power and control electronics components 114 ofthese machines essentially consume the entire back face area of themachine's rear frame 110, and does not permit sufficient axial air flowpast the electronics for air cooling them. Heat from the power modules116 must travel along the back face plane before reaching the coolingfins, which are located outside of the power modules. This traveldistance adds thermal conduction resistance and raises the temperatureof the power devices 116 accordingly.

Moreover, fins for cooling the power modules of these prior machines arenot in an area of high velocity inlet air flow, and/or do not work inconcert with the natural flow path of the incoming air, instead raisingair flow resistance and thus lowering overall bulk cooling air flowrates.

According to another prior cooling approach, the power electronics 116and control electronics 118 are spaced axially apart in the machine 100and cooling air is drawn through radial inlets into the machine beforeturning and flowing axially within the machine. This type of layout,however, induces high pressure drops due to turning the cooling airflow, and thus reduces the bulk air flow rate. This layout also promotesrecirculation of hot air exhausted from the rear of the machine 100 backinto its radial cooling air inlets. This recirculation effectivelyraises the temperature of cooling air drawn into the machine 100, thusraising component temperatures. These problems are overcome in anelectric machine 130 according to the present disclosure.

Relative to the power module orientations in prior electric machines 100(see, e.g., FIG. 2), the power modules 154 attached to the cooling tower158 are turned on edge, which provides many design advantages. Referringto the exemplary embodiments of FIGS. 4-7 and 11-25, the electronicpackage 132 includes a metallic cooling tower 158 defined by an axiallyextending first wall 160 that extends between axially opposite first 162and second 164 ends thereof and about the package central axis 168 suchthat, in an axial view (FIG. 20), the cooling tower 158 is shaped likean extruded polygon with finned surfaces or ribs 170 extending inwardlyof the cooling tower from the radially inner surface 172 of the firstwall 160. The cooling tower may, for example, be an aluminum casting orextrusion of which the first wall 160 and the ribs 170 are integrallyformed members. In the exemplary embodiments, the package central axis168 and the machine central axis 138 are coincident when the electronicpackage 132 is installed as a component of machine 130. The axiallyopposite first wall ends 162, 164 respectively define the first andsecond axially opposite ends 162, 164 of the cooling tower 158. Anaxially extending air passage 174 is defined by the radially innersurface 172 of the first wall 160.

On the radially outer surface 176 of the cooling tower structure 158,the power modules 154 are mounted on the flat polygon surfaces, whichdefine mounting pads 178 for the power modules 154. The mounting pads178 are evenly distributed circumferentially around the radially outersurface 176 of the cooling tower 158. For example, the mounting pads maybe generally equiangularly distributed about radially outer surface 176.The cooling tower 158 defines a main heat sink 180 for the power modules154, which are in conductive thermal communication with the mountingpads 178. The cooling tower ribs 170 extend inwardly directly away fromthese power module mounting surfaces 178. In the depicted embodiment,radially inward of the first wall 160 is a second wall 182. The firstwall 160, the second wall 182 (included the depicted embodiment), andthe ribs 170 are integrally formed members of the metallic cooling tower158. The second wall 182 extends axially between opposite first andsecond axial ends 162, 164 of the cooling tower 158, and about thepackage central axis 168. In an axial view, the second wall 182 definesanother hollowed polygon whose radially inner surface 184 defines aspace, or well 186, that serves as the location for the controlelectronics 188. In the depicted embodiment, the well 186 is bottomlesswithin the cooling tower 158, and has an axially projecting profile thatmay, for example, be polygonal though it is to be understood that inother embodiments, the well 186 structure can be of different shape ordepth, or be omitted altogether.

The cooling tower 158 has a generous cross sectional area in planesperpendicular to the central axis 168 along the length of the electronicpackage 132. Where used with an air-cooled machine 130, axial air flowalong the air passage 174 extending through the cooling tower 158 isuniform and near the radial center of the machine 130, which works wellwith the natural air flow pattern in machines of dual internal fanconstruction; optimal performance in such machines results from thecooling air entering the rear fan 148 axially through the insidediameter of the fan blades. Furthermore, the heat sink 180 has fins orribs 170 traversing the air passage 174, between which cooling airflows. The ribs 170 extend radially inwardly from the angular locationsof the power module 154 mounting locations, and also extend axiallybetween the air passage inlet 190 and outlet 192, which are defined atthe respective, axially opposite first 162 and second 164 ends of thecooling tower 158. The ribs 170 provide a large surface area from whichheat is convectively transferred to the cooling air, which yieldssuperior air cooling performance. The fins or ribs 170 of the heat sink180 extend radially inwardly toward the central axis 168 of the coolingtower 158 from the mounting pad location of each respective power module154. The ribs 170 of the cooling tower 158 are positioned directly inthe high velocity air flow of cooling air entering the rear of theelectronic package 132, and are arranged in concert with the naturalflow path of air entering the air passage 174 through its inlet 190 nearthe first axial end 162 of the cooling tower 158.

A cooling tower 158 according to the present disclosure providesmaximized spatial dispersion of the individual MOSFETs both angularlyabout the central axis 168 and in the axial direction. Maximizingspatial dispersion between the power electronics devices 154 tends tominimize their thermal conduction interaction and resulting devicetemperature.

The cooling tower 158 provides a large degree of dispersion of theindividual power modules 154, which serves to minimize their thermalinteraction and reduce their temperatures. This dispersion is a functionof the cooling tower geometry, which in the exemplary embodimentscircumferentially distributes six power modules 154 equally about theradially outer surface 176 of a cooling tower first wall 160 thatextends between the axially opposite ends 162, 164 of the cooling towerand about the central axis of the electronic package. Ideally, heat losssources, such as multiple MOSFET modules 154, are spread as far apartfrom each other as possible to minimize their conductive thermalinteraction. In an electronic package 132 having a cooling tower 158 asdisclosed herein, the individual MOSFETs are substantially equallyspaced over a 360 degree arc about the central axis 168 of the machine130. Further, the positive 194 and negative 196 MOSFETs within eachpower module 154 are widely separated in the machine's axial direction.

The depicted cooling tower embodiment provides a hollowed space or well186 for control electronics packaging appropriately in the radial centerof the main heat sink 180. This central location maximizes distancesbetween the control electronics circuitry 188 and each power module 154.It also locates control electronics circuitry 188 in an optimal area forcooling, this area being furthest from the power module heat sources.Positioning the control electronics 188 at this location also maximizesavailable space utilization by locating the control electronics, whichrequire relatively less cooling than do the power modules 154, directlybehind the rear bearing of the electric machine 130. In some air-cooledmachine embodiments, this area is in an air flow dead space, i.e.,portion of an air passage through which no air flow would otherwiseoccur. In other words, air would not flow through this space but for thepresence of the electronic control circuitry 188.

Thermal benefits also result from locating the control electronics 188near the radial center of the electronic package 132 and axiallyrearward the power electronic device positions. Cooling air enters thecooling tower 158 in an axial direction from the rear axial end 162 ofthe electronic package, and is drawn forward through the air passage174, towards the rear frame of the machine 130. Positioning theelectronic control circuitry 188 at this location, the coldest possibleair is available for cooling its components, which typically are lowertemperature rated. Moreover, since the control electronics 188 producerelatively little heat relative to the power electronics or themachine's stator 142 and rotor 140, the control electronics do notincrease the temperature of the cooling air in a meaningful way that isharmful to the downstream components.

Further, having the control electronics 188 in the center of theelectronic package 132 maximizes the physical distance to its typicallylower temperature rated components from the heat-producing MOSFETs,which are higher temperature rated. Since the waste heat from theMOSFETs is removed by the finned surface areas of the cooling tower 158,the heat sink surfaces around the control electronics 188 will be coolerthan those near the MOSFETs, which is beneficial for the controlelectronics.

Centrally locating the control electronics 188 also minimizes theelectrical signal transmission distance between the control electronicsand power electronics 152, which beneficially minimizes electrical noiseissues and cabling costs.

The radially outer surface 178 of the second wall 182 of the depictedembodiment is connected to the radially inner surface 184 of the secondwall through the ribs 170, some of which define radial spokes extendinginwardly from angular locations between circumferentially adjacent powermodule mounting sites. The first 160 and second 182 walls and the ribs170 are integrally formed as an aluminum casting or extrusion, and aretherefore in conductive thermal communication with each other. The axialair passage 174 is defined between the first and second walls, which istraversed by the ribs. The axial cross-sectional shape of the airpassage 174 is generally annular between the opposite axial ends 162,164 of the cooling tower 158.

The depicted cooling tower and power module layout works well withtypical alternator construction. It allows the ambient cooling air toflow axially into the machine 130 near the central axis 138 with a verygenerous and angularly uniform inlet area, but at the same time providesa large surface area for mounting and conductive cooling of the MOSFETmodules 134.

The cooling tower 158 beneficially facilitates a very uniform flow ofcooling air into the rear of the electronic package 132. The typicalelectronics layout of prior air-cooled electric machines 100 isgeometrically asymmetrical in an angular sense and has areas from whichcooling air flow is completely blocked, as is apparent in the example ofFIG. 2. Non-uniformity of the cooling air flow stream resulting fromsuch air flow blockage can create hot spots on the stator 104 of theelectric machine 100, which in turn lowers the temperature capabilityand/or performance of the machine. In comparison, the greater uniformityof the electronics layout in the electronic package 132 provides arelatively uniform air inlet area to the cooling tower 158, and acooling air flow therethrough that is much more uniform, minimizing thepossible occurrence of hot spots on the stator 142.

The mounting direction of the power modules 154 being perpendicular tothe orientation of the rear frame member 134 greatly minimizes the areathe modules axially project onto the back face 144 of the machine 130.Orienting the generally flat power modules 154 such that they areedge-wise to the back face 144 when mounted, or substantially parallelto the central axis 168, better allows packaging of a MOSFET modulenumber and size required for a desired electric machine design, and muchgreater design flexibility, vis-à-vis the electronics layouts of priorelectric machines.

By virtue of cooling tower ribs or fins 170 being in the cooling streamof incoming air flow and radially extending inwardly from locationsdirectly inward of the power module mounting locations 178, minimalthermal conduction resistance exists between the power devices 154 andthe cooling tower fins 170.

A cooling tower structure 158 according to the present disclosure allowscooling air to enter axially into the electronic package 132 withminimal restriction and a high degree of angular uniformity.

In electric machine embodiments 130 of dual internal fan construction,cooling air must enter the rear centrifugal fan 148 at its inner bladediameter for the fan to function properly, and a cooling tower structure158 according to the present disclosure lends itself naturally to thistype of flow. External fan machines 130, typical of current heavy dutyalternators, also work well with this cooling tower structure, as theair can flow through the air passage 174 and into the rear of themachine 130 with little flow restriction.

The exemplary cooling tower geometry is also compatible withliquid-cooled applications. In such applications, the back face 144 ofthe electric machine 130 is liquid cooled and the cooling tower 158 ismounted directly on this liquid cooled surface. The cross sectional areaof the cooling tower's integrally connected, thermally conductivemembers 170 allows the heat to flow conductively through the coolingtower 158 from the MOSFETs to the back face 144 surface, from which iscan be convectively removed by the liquid coolant circulating through awater jacket 146 defined by the frame's back face member 144. In otherwords, the relative large cross sectional areas of the cooling towerwall 160 defining the outer wall surface 176, and ribs 170, provide alow conductive thermal resistance for transferring waste heat from theMOSFETs to the back face surface. In addition, natural convectionadditionally occurs from the rib surfaces of the heat sink, whichfurther serves to remove the waste heat. Thus the cooling tower 158 iscompatible with both air and liquid cooled electric machines 130.

Beneficially, the electronic package 132 is adapted for attachment tothe rear frame member 134 of an electric machine 130 via the coolingtower 158, which is the main heat sink for the power modules 154. Thebase plates 200 of the power modules 154 and the module mountinglocations 178 on the cooling tower 158 are directly insurface-to-surface contact, whereby they are in conductive communicationelectrically and thermally. Because the module base plates 200 and thecooling tower 158 are electrically at ground potential, the coolingtower can be attached directly to the rear frame of the machine.

This is characteristic of the electronic package 132 is important forliquid-cooled applications, wherein the generous cross section of theheat sink 180 in planes perpendicular to the central axis 138 of themachine 130 facilitates the heat, transferred from the power devices 154to the cooling tower 158 through their contacting mounting surfacesalong a primary cooling path 202, to be further conducted along theprimary cooling path 202 to the back face 144 of the electric machine130. The back face 144 is formed on a rear frame member 134 and definesthe rearwardly facing surface of the machine housing. In liquid coolingelectric machines 130, the back face frame member 134 typically definesa liquid coolant passage 146. Heat is transferred convectively from theback face frame member 134 to the liquid coolant flowing through thewater jacket 146. Heat conducted from the cooling tower 158 to the backface 144 is removed by convection to the cooling liquid that iscirculated across the back face member 134 of the frame.

Yet another machine topology that can utilize electronics packagingaccording to the present disclosure is an air-cooled electric machine130 that has axially directed air flow substantially along the insidesurface of the machine's outer frame diameter. In an embodiment of sucha machine according to the present disclosure, both the liquid-cooledand air-cooled modes of cooling are employed. First, some of the heatfrom the MOSFETs is removed from the extensive surfaces of the coolingtower heat sink ribs 170 through convection to an axial flow of coolingair, as in an embodiment of a machine having dual internal fans.However, since the air must bend internally of the machine, at a pointdownstream of the cooling tower 158 and rear frame member 134interconnection location, a pressure drop is introduced to the coolingair that lessens its flow and therefore its cooling capabilities.However, just as with liquid-cooled applications, the generous area ofthe heat sink 180 in axial cross sections all along the central axis168, allows the remaining portion of the heat transferred to the coolingtower heat sink 180 from the MOSFETs along the primary cooling path 202to be conducted further along the path through the cooling tower 158,and into the rear frame member 134 of the electric machine 130, whichcan have additional surface finning to promote convective heat transferto the cooling air, and/or openings to allow establishment of a parallelair flow path, so that sufficient cooling air enters into the machinefor cooling of the machine's stator and rotor.

A cooling tower 158 according to the present disclosure offers a highamount of surface area for a given package size at the center of thestructure that works in harmony with the natural cooling air flow streamdirection in air-cooled machines.

The geometrical design and layout of a cooling tower according to thepresent disclosure provides an electronic package 132 compatible withair-cooled and/or liquid-cooled machines 130.

The cooling tower 158 provides a very rigid and stiff support structurefor the electronics to be mounted on. The cooling tower's stiffness isbeneficial for engine-mounted electric machine applications, wherevibration is a significant concern. The rear frame members 110 of priorelectric machines 100 are typically subjected to various modes ofbending and distortion when in use on an engine due to engine vibration.Axial oscillation of the rotor assembly mass, and forces on the shaftinduced by dynamic belt loading on the drive pulley, exert gyratingforces on the rear bearing, thereby inducing dynamic forces on themachine's rear frame member 110, which supports the rear bearing. Inprior electric machines 100, these bending modes create movement of theelectronic components 114 relative to each other and can cause componentfatigue failures, especially of connecting straps and the like.

In an electronic package 132 according to the present disclosure, all ofthe electronics are mechanically tied directly to the cooling towerstructure 158 and are not subject to the bending modes of the rear framemember 134. The integrally finned structure of the cooling tower 158,though primarily for cooling purposes, also intentionally serves toprovide mechanical stiffness to the cooling tower structure. The axiallength of the cooling tower, its 360 degree profile about its centralaxis 168, and its integral ribs 170 combine to provide an electronicpackage 132 according to the present disclosure relatively superiorstructural stiffness. Consequently, movement of the electroniccomponents mounted to the cooling tower relative to each other isminimized, and the comparative vibration robustness of an electronicpackage as disclosed herein is greatly improved relative to theintegrated electronics assemblies used in prior electric machines.Moreover, the rear frame member 134 of an electric machine 130 isadvantageously stiffened by the attachment of the cooling tower 158thereto. The stiffening of the rear frame member 134 minimizes itsbending and distortion, which can in turn minimize other fatigue-relatedfailures in the machine, such as throughbolt failure due to bendingfatigue.

The highly rigid structure of the cooling tower 158 results from itshaving an profile extending 360 degrees about the central axis, andinterlacing fins 170 that act as stiffening beams.

The cooling tower 158 is structurally rigid and minimizes vibrationconcerns since all power MOSFETs are mounted directly to it. Moreover,the rear frame member 134 of the electric machine 130 is also desirablystiffened by the electronic package 132 being mounted to the framemember 134 through the rigid cooling tower 158.

The control electronics 188 are tucked into the body of the main coolingtower heat sink 180, which minimizes the axial space required by theoverall electronic package 132. The central mounting location of thecontrol electronics assembly minimizes air flow blockage, minimizesexposure of the control circuitry to heat losses from the powerelectronics, exposes the control electronics to the coolest cooling airentering the electric machine 130, and minimizes the electrical signaltransmission distance between the control electronics 188 and the powerelectronics 152, which minimizes electrical noise problems and cablingcosts.

In an exemplary embodiment of the electronic package 132 the MOSFETs194, 196 and the MOSFET driver 204 contained in each power module 154are in conductive thermal communication with the cooling tower heat sink180, about which the modules are circumferentially distributed.Conductive heat transfer to this main heat sink is the primary coolingpath 202 for each MOSFET module 154. Beneficially, the positive (or highside) 194 and negative (or low side) 196 power devices (MOSFETs) of eachpower module 154 beneficially share a common module heat sink. Thisdesirable feature results from both the positive and negative MOSFETs194, 196 being identical N-channel devices with the same polarity and,in the exemplary embodiment depicted, providing a thin layer 206 ofthermally conductive electrical insulation that extends over the entireinterior surface 208 of the metallic module base 200, as shown in FIG.25. The thin electrical insulation layer 200 has low thermal resistance,and may be an existing, commercially available material such as, forexample, Thermal Clad™, commonly referred to as “T-Clad”, a product ofHenkel Corporation (www.henkel.com) and formerly from The BergquistCompany of Chanhassen, Minn., USA.

In one embodiment, the insulation layer 206 is printed on a surface 208of the module's heat-sunk metallic base 200. Atop this insulation layer206 is printed a copper trace or strip (not shown). Referring to FIG.26, a much thicker strap 210 of copper suitable for the current levelsconducted through the power modules 154 is soldered to the printedcopper strip, and the positive MOSFETs 194 are attached directly to thecopper strap 210. Within each module 154 the drains of the positiveMOSFETs are connected to the copper strap 210.

As noted above, the exemplary electronic package 132 utilized twoparallel-connected sets 156 a, 156 b of three MOSFET power modules 154.Amongst the three, circumferentially adjacent modules 154 of the firstset 156 a, which are respectively in communication with an associatedconductor 212 a of the stator's first winding set 214 a, the copperstraps 210 are interconnected to form a daisy-chained first power bus216 a. Likewise, amongst the three, circumferentially adjacent modules154 of the second set 156 b, which are respectively in communicationwith an associated conductor 212 b of the stator's second winding set214 b, which is shifted 30° relative to the first winding set 214 a, thecopper straps 210 are interconnected to form a daisy-chained secondpower bus 216 b. The first and second power buses 216 a, 216 b areinterconnected at the machine's B+ terminal 218, which is a component ofthe electronic package 132.

Similarly, another, parallel copper trace or strip (not shown) isprinted atop the insulation layer 206. Referring again to FIG. 26, amuch thicker copper member 220 suitable for the current levels conductedthrough the power modules 154 is soldered to this printed copper strip,and the negative MOSFETs 196 are attached directly to the copper member220. Within each module 154, the drains of the negative MOSFETs 196 andthe sources of the positive MOSFETs 194 are electrically connected tothe copper member 220. The copper member 220 of each power module 154extends from its module housing 222 to define the respective module'sphase connection terminal 224, to which the respective stator winding212 b associated with that power module 154 is connected via a phaselead wire.

The source of each negative MOSFET 196 is electrically connected to itsmodule's metallic base 200, and is grounded through the base and therespective mounting pad 178 of the cooling tower 158 to which the modulebase is attached. The MOSFET driver 204 of each power module 154 ismounted directly to the electrically insulative layer 206, and is incommunication with the control circuitry 188 via a respective signallead 226.

As mentioned above, its ability to share a common main heat sink 180 atground potential for the positive 194 and negative 196 MOSFETS of itsplurality of power modules 154, rather than requiring separate positiveand negative heat sinks at different potential levels as is typicallydone for the power electronics devices 116 of prior electric machines100, provides the inventive electronic package 132 substantially greaterdesign flexibility, vis-a-vis prior integrated electronic packages 114,to accommodate convection for air cooling, and/or conduction for liquidcooling via the back face 144 of an electric machine's rear frame.

Typically, the power electronics side of the phase connection to statorwinding phase conductor 212 a, 212 b is in a fixed, rigid position. Atypically-sized automotive alternator has a generally circular frameoutside diameter of 140 mm. With reference to FIG. 2, the power modulephase terminal connectors 120 in a prior electric machine 100 areradially located such that it can accommodate a narrow range of machinesizes, such as 129 to 144 mm stator outside diameter.

A slot or recess (hereinafter “void”) 228 provides clearance forpackaging the respective phase lead wire 230 defined by a phaseconductor 212 a, 212 b of the stator winding that extends between thestator 142 and the associated power module phase terminal connector 224.Providing these voids 228 in the rear frame back face 144 and/or theelectronic package's cooling tower 158 allows identical electronicpackage embodiments 132 to accommodate relatively larger variations inthe radial position of the stator phase conductors 212 a, 212 b. Thus, asingle electronic package 132 size may be utilized in electric machines130 of various stator sizes, including sizes so small as to radiallyposition the location 232 of stator phase conductor egress from the backface 144 inside the perimeter of the cooling tower axial end 164attached to the back face 144, though the module phase terminalconnector 224 locations are outside of that perimeter.

Prior electric machines 100, which have electronic package layouts inwhich MOSFET modules 116 are mounted to back face 112, with the modulebase mounting surfaces disposed in a plane perpendicular to the centralaxis 108, as shown in FIG. 2, cannot feasibly provide such voids nearthe module phase lead connector terminals 120, because the voids wouldbe at the modules 116 themselves. It is desirable to accommodate abroader range of machine sizes, however. For instance, the designrequirement desired for an embodiment of an electronic package 132according to the present disclosure calls for accommodating a range ofstator machine diameters ranging from 120 mm up to 190 mm.

However, the MOSFET modules 154 being mounted to the cooling tower 158at circumferentially distributed locations about the central axis 138,and in planes parallel with the central axis, provides a recess 228between circumferentially adjacent power modules 154. The cooling towerribs or fins 170 in this area can be removed without a large detrimentalthermal issue since the location lies in a naturally occurring adiabaticplane.

Via axial location of the MOSFET module 154 afforded by the coolingtower 158, there is some axial space 234 between the phase leadconnection 224 and the back frame 144 of the electric machine 130. Thisyields valuable length between the stator end turns and the phaseconnection at the phase terminals 224 of the MOSFET module 154 for thestator conductor 230 to be routed and radially transition between thetwo locations relative to the machine shaft's axis of rotation 138.

An electric machine embodiment 130 according to the present disclosureprovides a slot opening or recess 228 in either or both of the coolingtower heat sink 180 and the rear frame 134, 144 of the electric machine130, in the area between circumferentially adjacent power modules 154.

Certain exemplary electric machine embodiments 130 are provided with aplurality recesses or slots (“voids”) 228 circumferentially distributedalong the corner 236 formed between the cooling tower's forward axialend 164, which interfaces and is attachable to the machine's rear framemember 134, 144, and radially outer surface 176. Each void 228 iselongate in a radial direction and defines a recess opening axiallyforward, in the axial end surface 164 of the cooling tower 158, andradially outward at locations between circumferentially adjacent powermodules 154, which are attached to mounting locations 178 on the coolingtower's radially outer surface 176. Each void 228 extends radiallyinwardly from the radially outer wall surface 176 to radial positionsalong the length of the void 228 that coincide with the phase conductorpass through locations 232 for machines 130 of various small sizes.

Referring to FIG. 30, some electric machine embodiments 130 includingsuch an electronic package 132 are of sufficiently large diametric sizethat their stator winding phase conductors 230 extend through the rearframe member 134 at locations 232 radially proximate or outward of themodule phase terminal connectors 224. In such machines the phaseconductors 230 are directed radially inward from their respectiveapertures 228 to be connected to the associated module phase terminal224.

Referring to FIG. 31, other electric machine embodiments 130 include anidentical electronic package 132 and are of relatively smaller diametricsize. The phase conductors 230 extend through the rear frame member 134at locations radially inward of the module phase terminal connectors224, and perhaps at radial positions inside the void 228. In suchmachines the phase conductors 230 are directed radially outward fromtheir respective apertures 232, along the void 228. The void 228 issized for routing the phase conductor 230 to the power module phaseterminal 224, with clearance to the cooling tower 158 and the back face144 to facilitate connection to the associated module phase terminal224. In such machines, wherein the forward axial end 164 of the coolingtower superposes the phase lead wire egress location 232, the windingphase conductor (or phase lead wire) 230 can be routed radially alongthe void 228 with sufficient clearance to avoid wire damage and provideproper seating of the cooling tower 158 to the rear frame member 134.

In other embodiments, the electronic package 132 may or may not includevoids 228, but the back face 144 is provided with an aperture 228elongated in the radial direction through which the phase conductor 230can exit the back face at positions 232 affording sufficient clearanceto the cooling tower forward axial end 164.

With ample space 234 for a simple phase lead terminal structure 224having a wrap-around strap coming from the MOSFET module 154, phase leadwires 230 of varying cross section can be accommodated. The connectionis completed by soldering or welding the connection.

A one-piece molded plastic guide (not shown) provides the necessaryelectrical isolation between the stator winding phase conductor/phaselead wire 230, and the frame 134, 144 and the metallic cooling tower158. This guide/insulator is simply trapped between the cooling towerand rear frame during assembly to hold the insulator(s) in position.

The exterior surface 238 of each power module cover plate 240 facesradially outward and is unobstructedly exposed to ambient airsurrounding the electronic package 132. This facilitates convectivetransfer of heat generated by the power electronics devices 154 to theair surrounding the electronic package through the cover plate 240. Thecover plate exterior surface 238 is configured, e.g., with fins 242, toenhance convective heat transfer therefrom to the ambient air. Anelectronic package embodiment 132 according to the present disclosure isthus provided with bi-directional cooling of each power module 154 inopposite radial directions.

The MOSFET modules 154 are mounted to the cooling tower structure 158such that bi-directional cooling of the power electronics can bemaximized. Heat loss from each power module 154 initially follows aprimary cooling path 202 radially inward through the module base 200 andinto the main heat sink 180 defined by the cooling tower 158 at themodule mounting location, from which the respective cooling fins 170extend radially inwardly. Heat loss from each power module 154 alsoinitially follows a respective secondary cooling path 244 radiallyoutward through its cast aluminum cover plate 240, and to the ambientair through the cover plate's finned exterior surface 238. Thebi-directional cooling paths 202, 244 from the power electronics devices194, 196, 204 of each module 154 minimize the thermal resistance to heatflow from the power electronics devices housed therein. Heat loss fromthe plurality of power modules 154 collectively also follows radiallyinward and radially outward primary 202 and secondary 244 cooling paths,relative to the electronic package 132. The primary and secondarycooling paths are parallel paths, rather than sequential paths.

The radially inwardly facing interior surface 246 of each module coverplate 240, which is exposed to the MOSFETs 194, 196 and the MOSFETdriver 204 within the module 154, is provided with integrally castbosses 248 that extend radially inwardly toward the MOSFETs and theMOSFET driver. Relative to each power module 154, the cast aluminummodule cover 240 and its integral bosses 248 define a heat sink for heatloss from the power electronics devices, and the secondary cooling path.From an electrical standpoint, the cast aluminum cover 240 cannot touchthese electronic components or their wire bonds, and so the boss 248surfaces are spaced therefrom. Disposing the boss surfaces as close aspossible to the MOSFETs 194, 196 and the MOSFET driver 204 whilemaintaining gaps therebetween, however, enhances the overall cooling ofthe power modules 154. Heat transfer to the boss surfaces couldpotentially be enhanced by further minimizing the gap between the bosses248 and the MOSFETs 194, 196 and/or the MOSFET driver 204. Such amodification could entail lengthening the boss 248 and slightlyplastically deforming the natural arc or bend in the wire bonds to theMOSFETs and the MOSFET driver through use of a simple axial press and anappropriate shaped tool. Minimize the gaps between these devices and theheat sink would reduce the conduction temperature drop along thesecondary cooling path, and therefore further reduce the devicetemperature.

Although the MOSFET driver 204 produces very minimal heat in comparisonto the MOSFETs 194, 196, it is important to maintain the drivertemperature as low as possible. Each MOSFET has a targeted operatingtemperature in the 150° C. range. Because the MOSFET driver is packagedwith the MOSFETs in the power module housing 222, without specialprovisions made for cooling the driver 204, it would also be subject toan environment in the 150° C. range since it is surrounded by surfacesgenerally at this higher temperature.

Ambient cooling air surrounding the electric machine 130 is typically inthe 125° C. range. Bi-directional cooling for the MOSFET driver 204 inthe power module enables cooling the MOSFET driver to temperatures lowerthan the MOSFET temperatures. By positioning the integrally-formed boss248 extending from the interior surface 246 of the cast aluminum modulecover plate 240 into close, spaced proximity to the MOSFET driver, heatfrom the space immediately about the driver, including heat loss fromthe driver itself, is transferred to the boss 248 surface and conductedalong the secondary cooling path 244 to the exterior cover plate surface238, from which it is convectively lost to the ambient air. The MOSFETdriver can thus be cooled to a temperature lower than the bulktemperature around the driver 204 and close to the ambient airtemperature, thereby improving the driver's reliability.

A secondary benefit of providing the cast aluminum cover plate 240 withthe integral bosses 248 is that the bosses serve to increase thermalcapacity. Bi-directional transient cooling is provided by the increasedthermal capacity provided by the cast aluminum bosses. In use, a powermodule 154 is not only subject to continuous electrical operation but,by the nature of the product and its usage, also experiences peak useconditions. Under such conditions high transient electrical loadingoccurs, during which the devices 194, 196, 204 are typically at theirgreatest temperatures. The high transient electrical loading thereforetranslates into high transient thermal loading, which can undermine thereliability of the power electronics devices. The mass of the main heatsink 180 portion in the vicinity of the power module mounting locations178 significantly helps absorb the transient thermal energy, but themass of the cast aluminum cover plate bosses 248, whose surfaces arepositioned in close proximity to the power electronics devices 194, 196,204 and form parts of the secondary cooling path 244, also helps absorbthe transient thermal energy and keep the devices relatively coolerduring machine operation under peak use conditions. From a thermalcapacitance perspective, a thermal capacitor is thus effectivelyprovided radially inwardly and radially outwardly of the powerelectronics components of each MOSFET module, and serve to absorb thethermal transients.

The bi-directional cooling facilitated by the cast aluminum module coverplate 240 also helps achieve a common electronic package designembodiment to be used for both air-cooled and liquid-cooledapplications. Such embodiments are necessarily sub-optimized thermallyrelative to each cooling medium individually to allow the physicallayout and design of the electronic package 132 to remain common.However, removal of some of the waste heat from the power MOSFETs 194,196 via the secondary cooling path 244 lessens the requirement for heattransfer therefrom via the primary cooling path 202. The removal of aportion of the generated heat through the module cover plate 240 via thesecondary cooling path 244 helps minimize compromises that sub-optimizecooling performance relative to each medium individually, andfacilitates providing a common electronic package 132 design that meetsthe thermal requirements of both cooling media.

Bi-directional cooling of the power electronics devices beneficiallyallows identical embodiments of an electronic package 132 according tothe present disclosure, to be used in both air-cooled and liquid-cooledelectric machines 130. Bi-directional cooling of each power module 154is provided by the power module being mounted in thermally conductivecontact to the main heat sink 180. The main heat sink in turn transfersheat received from the power electronics devices to an air or liquidcooling medium. Bi-directional cooling of each power module 154 is alsoprovided by the finned, cast aluminum module cover plate 240, whichtransfers heat received through bosses 248 from the power electronicsdevices, convectively to ambient air.

In other words, MOSFET cooling along the primary cooling path 244 isinitially by conduction through the power module mounting surface 178 ofthe main heat sink 180, and subsequently by convection from the mainheat sink 180, or an electric machine rear frame member 134, 144 towhich the cooling tower 158 is attached, to an air or liquid coolingmedium. MOSFET cooling along the secondary cooling path 244 is initiallyby conduction through the module cover plate 240 heat sink, andsubsequently by convection to ambient air from the fins 242 formed onthe outside surface 238 of module cover plate 240.

As discussed above, placement of the electronic control circuitry 188 ata radially central location in the cooling tower air passage 174 inair-cooled electric machine embodiments 130, particularly in electricmachine embodiments exhibiting an air flow dead zone, minimizes thenegative impact on air flow due to blockage. Minimizing the axiallyprojected area of the radially centrally positioned control electronics188 in air-cooled electric machine embodiments can, however, provideimprovements to the air flow through the cooling tower 158, particularlyin machine embodiments 130 not characterized by an air flow dead space.

To this end, certain embodiments of an electronic package according tothe present disclosure include electronic control circuitry 188 havingcircuit board material portions 250 turned on edge relative to theirtypical orientation in prior electric machines 100, so as to extend indirections substantially parallel with the cooling tower central axis168. In other words, the control circuitry portions 252 of suchembodiments are oriented substantially perpendicularly relative to agenerally planar back face 144 of the rear frame. This orientationallows the electronic control circuitry 188 to be contained within aminimal axially projected area, near the radial center of the coolingtower 158.

In the depicted embodiment, electronic control circuit portions 252 sooriented are disposed within a plastic cup or receptacle 254 defined bya floor 256 and enclosing side walls 258 that extend along the radiallyinner surfaces 184 of the second cooling tower wall 182 that defines thewell 186. In this embodiment, the axially forward surface 260 of thereceptacle floor 256 is substantially flush with the second axial end164 of the cooling tower 158, which is adapted for attachment to a rearframe member 134, 144 of an electric machine 130. The receptacle floor256 of this embodiment is recessed to receive the rear axial end of therotor shaft and a brush holder. The side walls 258 of the receptacledefine an opening 262 over which a metallic lid or cover plate 264containing the regulator terminal 266, is mounted to enclose thereceptacle's interior space. The control circuitry 188, receptacle 254and cover plate 264 define a control electronics assembly 268. Thecontrol electronics assembly is mounted within and protected bysurrounding second wall 182 of the cooling tower 158. The receptacle 254may be made of glass-filled nylon, and thermally isolates the controlelectronics 188 from heat generated by and lost by the MOSFETs, bygreatly increasing the conductive thermal resistance therebetween. Thelid 264, however, is metallic and exposed to the oncoming cooling air toprovide heat sinking for control electronics components (such as thefield output device) which do produce a small amount of heat, generallyin the 5-10 watt range. Placing control circuit portions 252 includingthese types of control electronics components on the axially forwardlyfacing interior surface 270 of the receptacle lid 264 thermally isolatesthose components from the rest of the control electronics circuitry.

The construction of the control electronics assembly's cup 254 and lid264 provides protection for the control electronics 188 by shieldingthem from external splash and contaminants. It also reduces overall costby providing a protective housing for the electronics that does notrequire additional packaging or overmolding of the circuit board forprotection. In addition, the surrounding wall 182 of the cooling towerwell 186 provides means for mounting and protecting the controlelectronics assembly 268. As noted above, the well structure 186 can beof different shape or depth or be omitted altogether. Likewise,configuration of the control electronics assembly 268 may likewise beother than as shown.

While certain embodiments of the electronic package 132 includeelectronic control circuitry 188 utilizing only rigid circuit boardmaterial 250, certain other embodiments of the electronic package 132include electronic control circuitry 188 utilizing flexible circuitboard material 272. Such material is commercially available from, forexample, Minco Products, Inc. of Minneapolis, Minn., USA(www.minco.com). This material can yield the same type of properties anddesign flexibility, including multiple layers, as conventional, rigidcircuit board material. However, the flexible circuit board material 272can be bent, twisted, folded or otherwise deformed, and still performsubstantially like rigid circuit board material.

According to a first embodiment of this design, component hardboardsincluding control circuit portions 252 to be carried by the flexiblecircuit board material 272 are laminated to the flexible circuit boardmaterial. The flexible circuit board material 272 is produced withelectrically conductive traces or wires 274 through which conductors ofcontrol circuit portions 252 included on separate component hardboards250 may be electrically interconnected. In corners between adjacentrigid component hardboards 250, the flexible circuit board material 272(and its interconnecting conductive traces 274) is deformed tofacilitate hardboard positioning in different planes, thus allowing therigid component circuit boards 250 to be interconnected without the useof any pin type connectors and/or cabling.

In some alternative embodiments, the control circuitry layout is brokenup into multiple control circuit portions 252, which are thenprinted/assembled on flexible circuit board material 272 to be providedas a singular piece 276 of flexible circuit board material 272 in thecontrol circuitry 188. The electrically conductive traces 274 ofmultiple flexible circuit board layouts are printed on a sheet offlexible circuit board material substrate, the individual flexiblecircuit board material pieces 276 are then cut from the sheet. Similarversions of flexible circuit board material 272 may be produced thatvary in length and conductor configuration to accommodate optionalcontrol circuit portions, as indicated by the dashed outlines in FIGS.52 and 53. Referring to FIG. 54, the flexible control circuit material272 nests nicely in an undeformed state, which facilitates high materialutilization of storage and shipping containers.

Some embodiments take further advantage of the properties of flexiblecircuit board material 272 and the in these embodiments the controlcircuitry 188 includes integrally formed signal leads 278 between thecontrol circuitry 188 and the MOSFET gate driver 204. The signal leads278 include conductors 274 printed on the same, singular piece offlexible circuit board material 272 used for the control circuitry. Inother words, the signal leads 278 of flexible circuit board material 272extend to the various MOSFET gate drivers 204 and are simply bent intoposition along the wall of the molded plastic MOSFET module housing 222material. Connector bodies 282 can be added directly to the flexiblecircuit board material 272 at the terminal ends of the signal leads 278and their respective conductors 274. These connectors are then pluggedinto the MOSFET driver connector terminals 284 of respective MOSFETmodules 154 to complete the circuit. Thus, a separate wiring harnesscontaining signal leads for communicating the gate driver signals fromthe control circuit assembly 188 to the six MOSFET modules 154, and theseparate, associated wiring connections between that wiring harness andthe control circuitry, are eliminated.

A pedestal 286 of aluminum material is provided on the cooling towerfirst wall 160 where the MOSFET modules are mounted. Pedestal 286 can bemachined by the side edges of an axially moveable cutting tool, therebyproviding a simpler approach to forming a flat mounting surface andminimizing the thermal drop between the MOSFET modules 154 and the heatsink 180. The entire axial extent of the pedestal mounting surface canthus be cut at once by clamping the cooling tower 158 in an uprightposition at a milling station thereby allowing easy access to thepedestal mounting surfaces. In addition, at one fixed milling station, atool path can be set up to machine all pedestal mounting surfaces atonce.

Another benefit relating to this seemingly subtle, but rather importantdesign feature concerns the thermal aspects of the design. Theelectronic package 132 disclosed herein will be used in electric machine130 applications with very demanding transient loading on the powerelectronics, such as providing the starting torque for an engine.

With these short transient conditions, the high current and resultingtemperature increase can be best endured by providing sufficient thermalmass located as close as possible to the MOSFET to absorb the transientspike in heat generated during this period of time. The pedestal 286 ofadditional aluminum mass is provided to the cooling tower at themounting surface exactly where it is needed without adding massthroughout the entire peripheral surface of the cooling tower whichwould result in little benefit at additional cost. This also has asecondary benefit to increase the cross sectional area radially inwardof the MOSFETs where is it most needed for conductive heat spreading.Again, increasing the cross-sectional area of the heat sink further awayfrom the MOSFETs is comparatively less effective and would increase costwhile providing limited benefit. Through use of a separate pedestal foreach respective MOSFET module, the thermal conduction benefit ismaximized while minimizing the additional material cost.

Another subtle but significant benefit of the disclosed pedestalstructure is the electrical clearance it provides between ground and theB+ and phase lead conductors 216 a, 216 b, 230. By having each MOSFETmodule 154 mounted on a respective pedestal mounting surface 288 at anincreased radial distance from the radial outer surface of the firstwall 160, and then overhanging the plastic rear shroud 290 of theelectronic package around the module 154 and over the edge of itspedestal, the electrical clearance between the conductors 216 a, 216 b,230 and the grounded cooling tower heat sink 180 is increased directlyby the radial height of the pedestal 286.

Yet another benefit provided by the novel pedestal structure relates toimproved contamination and splash protection. Were the MOSFET modules154 mounted with base 200 flush against the exposed, radially innermost,portion of the power module mounting surface of the radially outwardlyoriented cooling tower heat sink surface, any encountered splash couldrun down the face of the heat sink, e.g., radial outer surface 176, androad contaminants in the splash could then directly span or bridge theradial distance from grounded portions of the module 154 or heat sink186 to locations where the conductors 216 a, 216 b, 224 exit the module,or result in contaminants being deposited along the edge of the MOSFETmodule base heat sink-to-cover interface. This could undesirably lead toroad contaminants entering into the MOSFET module(s) or result incurrent leakage from the module(s) or the conductors. By having eachpower module 154 mounted to the mounting surface of a radially outwardlyprojecting pedestal 286, with the module housing 222 having an overhungportion 296, a natural gutter 298 is formed that channels road splashaway from this area. Electrical clearances between the module conductors216 a, 216 b, 226 and the radially outer surface 176 is increased, whichminimizes the possibility of these detrimental occurrences. A portion296 of the plastic MOSFET module housing 222 extends beyond theperimeter of the pedestal 286 of the cooling tower heat sink 188 tocreate a ledge 300 which forms a natural gutter 298 that guides splashand provides drainage away from the area. The ledge 300 also lengthensthe path between the module's copper terminals 216 a, 216 b, 224 andground (i.e., the heat sink 180), and defines a geometry that is muchharder for a conductive trace (e.g., from contaminates such as roadsalts) to build up. Such a conductive trace can often lead to currentleakage problems.

The entirety of each pedestal 286 projects radially outwardly of theremainder of the tower structure 180, with its respective radiallyoutwardly facing, planar MOSFET module mounting surface 288 beingsubstantially parallel with the shaft axis. Thus, the tower is providedwith a plurality of discrete, circumferentially distributed pedestalsabout the central axis. The pedestals 286 are evenly distributed (e.g.,generally equiangularly) about radially outer surface of the coolingtower, and the module mounting surfaces are oriented tangentiallyrelative to an imaginary circle concentric with, and orientedperpendicularly relative to the longitudinal direction of, the axis.

The pedestal surface 288 for MOSFET module attachment providesadditional mass and cross sectional area for absorbing a thermaltransient, thereby minimizing thermal conduction spreading resistancefrom the heat source, and does so in a manner that minimizes the amountof material added, and facilitates the ease and speed of machining thepedestal surfaces to which the MOSFET modules are mounted.

The pedestal mounting surface 288 for each MOSFET module providesincreased separation, and electrical clearance, between the conductorsexiting the modules and the exposed surfaces of the cooling tower heatsink 180, which is at ground potential.

The pedestals 286 provide splash and contaminant protection for theMOSFET modules by creating gutters 298 to guide splash and directsplash-borne contaminants away from the modules 154, and provideseparation distances across which conductive traces of the contaminantsare less likely to build up, which reduces the likelihood of currentleakage from the modules.

While exemplary embodiments have been disclosed hereinabove, theinvention is not necessarily limited to the disclosed embodiments.Instead, this application is intended to cover any variations, uses, oradaptations of the present disclosure using its general principles.Further, this application is intended to cover such departures from thepresent disclosure as come within known or customary practice in the artto which this present disclosure pertains and which fall within thelimits of the appended claims.

What is claimed is:
 1. An electronic package adapted for connection to arear frame member of an electric machine, the electronic packagecomprising: a cooling tower having opposite first and second axial endsspaced along a package central axis, the cooling tower comprising: ametallic wall extending about the package central axis to define aradially inner wall surface and a radially outer wall surface, theradially inner wall surface defining an axially extending air passagethrough the cooling tower, the air passage having an inlet proximate thefirst axial end, and a plurality of spaced metallic ribs in conductivethermal communication with the radially inner wall surface, the ribstraversing the air passage; and a plurality of power electronics devicesattached in conductive thermal communication to the cooling tower atcircumferentially distributed positions on the radially outer wallsurface; wherein the cooling tower provides a heat sink for heat lossfrom the power electronics devices, and a primary cooling path for eachpower electronics device extends radially inwardly to the cooling towertherefrom.
 2. The electronic package of claim 1, further comprising aplurality of power modules, each power module comprising: at least onepower electronics device; a base in conductive thermal communicationwith the radially outer wall surface, and a metallic cover plate, thecover plate having an interior surface superposing the base and anexterior surface oriented radially outward and unobstructedly exposed toambient air surrounding the electronic package; wherein heat loss fromeach power module is transferred along the first cooling path and alonga secondary cooling path extending radially outwardly through the coverplate and to ambient air.
 3. The electronic package of claim 2, whereinthe module cover plates are configured with fins, whereby convectiveheat transfer therefrom is enhanced.
 4. The electronic package of claim1, further comprising: a plurality of power modules comprising theplurality of power electronics devices, wherein each power modulecomprises a base defining a surface that abuttingly engages the radiallyouter wall surface, whereby the base and the cooling tower wall are inconductive thermal communication, the engaging surfaces extendingsubstantially parallel with the package central axis.
 5. The electronicpackage of claim 4, wherein the plurality of metallic ribs extenddirectly from circumferential locations on the radially inner wallsurface that are directly radially inward of the power modules.
 6. Theelectronic package of claim 4, wherein the radially outer wall surfacedefines a plurality of planar mounting surfaces, each planar mountingsurface engaging the base surface of a respective power module, eachplanar mounting surface parallel with the package central axis.
 7. Theelectronic package of claim 6, wherein each planar mounting surface isoriented tangentially relative to an imaginary circle concentric withand oriented perpendicularly relative to the package central axis. 8.The electronic package of claim 1, wherein the wall and the ribs areintegrally formed portions of the cooling tower.
 9. The electronicpackage of claim 1, further comprising electronic control circuitryoperatively connected to the power electronics devices, the electroniccontrol circuitry substantially surrounded by the plurality of powerelectronics devices.
 10. The electronic package of claim 9, wherein thecontrol circuitry is substantially thermally isolated from the heat lossfrom the power electronics devices.
 11. The electronic package of claim1, wherein the power electronics devices are substantially evenlydistributed about the radially outer wall surface.
 12. The electronicpackage of claim 1, wherein the power electronics devices areequidistance along the package central axis from an imaginary planeperpendicular to the package central axis.
 13. An electric machinecomprising a stator defining a machine central axis, a rotor surroundedby and rotatable relative to the stator about the machine central axis,a rear frame member rotatably fixed relative to the stator and throughwhich the machine central axis extends, and an electronic packageaccording to claim 1, wherein the machine central axis extends throughthe electronic package and the cooling tower is connected to the rearframe member.
 14. The electric machine of claim 13, wherein the machinecentral axis and the package central axis coincide.
 15. The electricmachine of claim 13, wherein the electric machine is air-cooled and therear frame member has an aperture through which cooling air flow isdrawn generally axially, in the direction of the rotor relative to theelectronic package, for cooling the electric machine at locationsdownstream of the aperture, wherein the air passage has an outletproximate the second axial end, and the air passage outlet is in fluidcommunication with the rear frame member aperture, and wherein coolingair flow is drawn into the air passage inlet and through the airpassage, convective heat transfer along the primary cooling path occursbetween the cooling tower wall and ribs and the cooling air flow alongthe air passage, and the cooling air flow proceeds through the airpassage outlet and the rear frame member aperture for cooling theelectric machine at locations downstream of the aperture.
 16. Theelectric machine of claim 15, further comprising a fan rotatable withthe rotor about the central axis, wherein the air flow through theaperture is induced by fan rotation.
 17. The electric machine of claim13, wherein the electric machine is liquid-cooled and the rear framemember defines a metallic wall extending substantially perpendicularlyrelative to the machine central axis, the rear frame member wall havingan inner axial side in contact with liquid coolant and an opposite outeraxial side in conductive thermal communication with the cooling tower,and wherein conductive heat transfer occurs between the cooling towerand the rear frame member wall, and convective heat transfer occursbetween the rear frame member wall and the liquid coolant.
 18. Theelectric machine of claim 13, further comprising: a plurality of powermodules comprising the plurality of power electronics devices, whereineach power module comprises: a base in conductive thermal communicationwith the radially outer wall surface, and a metallic cover plate, thecover plate having an interior surface superposing the base and anexterior surface oriented radially outward and unobstructedly exposed toambient air surrounding the electronic package; wherein heat loss fromeach power module is transferred along the first cooling path and alonga secondary cooling path extending radially outwardly through the coverplate and to ambient air.
 19. The electric machine of claim 18, whereinthe module cover plates are configured with fins, whereby convectiveheat transfer therefrom is enhanced.
 20. The electric machine of claim13, further comprising: a plurality of power modules comprising theplurality of power electronics devices, wherein each power modulecomprises a base defining a surface that abuttingly engages the radiallyouter wall surface, whereby the base and the cooling tower wall are inconductive thermal communication, the engaging surfaces extendingsubstantially parallel with the machine central axis.